"We cannot discuss all the details of our efforts, but there should be no doubt that on a daily basis -- using our military, intelligence and diplomatic tools -- we work to see Sgt. Bergdahl returned home safely," the spokesman said.

His family, who received a letter from him last year via the Red Cross, issued a statement in response to the latest video.

"As we have done so many times over the past 4 and a half years, we request his captors to release him safely so that our only son can be reunited with his mother and father," the statement reads. "BOWE - If see this, continue to remain strong through patience. Your endurance will carry you to the finish line. Breathe!"

Bergdahl was 23 when he was captured after finishing a guard shift at a combat outpost in southeastern Paktika province.

The U.S. government acknowledged in May 2012 that it was engaged in talks with the Taliban to free Bergdahl.

The discussions moved in fits and starts because of U.S. concerns that any Taliban prisoners swapped for Bergdahl might be repatriated and allowed to rejoin the fight.

Later that year, however, the White House announced it was willing to send five Taliban prisoners to Qatar in exchange for Bergdahl.